Production of driving documents

Questions:

• Do the police need a reason to stop me whilst I am driving?
• I have got a fixed penalty notice, do I have to surrender both parts of my licence?
• I have got to produce my documents but I am away on holiday/ on business and do not have the documents, what should I do?
• I have received an endorsable fixed penalty ticket and need to send my licence off but I am going on holiday and need my licence, what can I do?
• I received a summons/conditional offer for a traffic offence through the post and lost it, what do I do?
• Is it an offence not to carry all relevant documents when driving so they can be produced for a police officer upon request?
• Now that the paper counterpart to my driving licence is no longer valid, how do I hire a car in the UK or when I go on holiday?
• What information do I need to provide to the DVLA if I sell my car?